Liquid medicament injector system
RELATED APPLICATION 
     This application is a continuation-in-part of application Ser. No. 254,262, filed on Oct. 5, 1988, now U.S. Pat. No. 4,902,279, issued 2/20/90, which is incorporated herein by reference. 
    
    
     BACKGROUND 
     The present invention is related to mechanisms for causing the needles on hypodermic syringes to penetrate the flesh and the plungers of the syringes to expel medicaments therefrom and through the needles into the flesh. While the invention is useful to physicians, paramedics, nurses or the like, it is particularly useful to patients who are required frequently to self-administer medicaments such as insulin in cases of diabetes. 
     Injector devices for facilitating hypodermic injections are known, both for medicament ampules that are furnished with the injector device, and for conventional hypodermic syringes that are operated by the device. In the case of injection from self-contained ampules, see, for example, U.S. Pat. Nos. 4,194,505, 4,316,463, and 4,413,991 to the present inventors, and U.S. Pat. No. 3,712,301 to Sarnoff. For injection from conventional syringes, see U.S. Pat. No. 4,494,358 to Fehlis, U.S. Pat. No. 3,702,608 to Tibbs, and U.S. Pat. No. 3,880,163 to Ritterskamp. 
     It is also known to provide a &#34;tracked&#34; injection wherein the medicament is caused to issue from the needle during movement of the needle into the patient&#39;s flesh for preventing tissue damage that would otherwise be caused by a &#34;balloon&#34; injection, wherein substantially all of the medicament is deposited after the needle reaches maximum penetration. 
     In clinical and home use applications such as for insulin injections, it is desirable to have a re-useable injector that incorporates a conventional syringe or the like for avoiding costs associated with discarding the ampule-type injectors after a single use. However, the injectors for conventional hypodermic syringes have other problems. For example, they are unreliable for accurate penetration and dosage because they are subject to operation with the syringe not properly seated in the device. Also, they are subject to inaccurate dosage due to loss of a portion of the medicament from the syringe prior to a necessary depth of needle penetration into the flesh. Moreover, they are subject to inadvertent premature actuation during attempts to engage the syringe with the injector device, consequently subjecting those nearby to possible injury. 
     A further problem with syringe injectors is that in case of a faulty injection, analysis of causation is clouded by the possibility of injector tampering, especially when the injector can be easily disassembled and improperly assembled by the user. 
     Thus there is a need for an injector device for a hypodermic syringe that reliably and safely facilitates administration of a precise medicament dosage without excessive tissue damage. 
     SUMMARY 
     The present invention is directed to a safety injector for medical syringes that meets this need. The syringe includes a cylindrical barrel having a syringe axis, a lateral projection on the barrel, a hypodermic needle having a tip extending a fixed distance relative to the lateral projection and carried by and in fluid connection with one end of the barrel, a fluid expelling plunger in the barrel and having a portion extending from an opposite end of the barrel. The injector apparatus includes an elongated body having a forward end for the needle and a rearward end portion of the extending portion of the plunger; a trigger member supported by the body and having a trigger surface projecting forward of the forward end of the body and being rearwardly movable from an extended position toward the body in response to pressure from the flesh of a user; receiver means for holding the syringe axially aligned with the body, including a guide member having a cavity for releasably holding the barrel of the syringe and having a lateral opening for radial movement of the barrel into the cavity; means for holding the syringe in lateral alignment with the body during insertion of the syringe into the receiver means, including opposite entry surfaces at a forward extremity of the guide member for laterally centering a contacted portion of the barrel, and rear guide means located rearwardly of the entry surfaces for laterally centering a rear portion of the syringe; stop means for limiting movement of the syringe in the body from a first position forwardly to a second position, the needle being located behind the trigger surface in the first position of the syringe when trigger member is extended, the needle projecting beyond the trigger surface for piercing the flesh of a user when the syringe is in the second position; actuator means for moving the plunger in a direction toward the forward end of the body; catch means for preventing operation of the actuator means; and release means connected to the trigger member for releasing the catch means, whereby the actuator moves the plunger forwardly in the barrel, the syringe being moved from the first position to the second position. 
     The rear guide means can include laterally spaced side guide surfaces of the rearward end portion of the body for engaging a downwardly projecting portion of the lateral projection on the barrel of the syringe as the syringe is moved forwardly relative to the body toward the first position with the barrel in contact with the entry surfaces. Also, the injector apparatus can include the syringe in an injection system. 
     Preferably, the syringe is formed to include a downwardly facing guide portion of the lateral projection, and the rearward end portion of the body is formed with a top guide surface, the top guide surface in combination with the entry surfaces of the forward extremity of the guide member defining a longitudinal rest inclination of the syringe relative to the body as the syringe is moved forwardly on the injector apparatus for facilitating entry of the syringe into aligned engagement by the receiver means. Preferably, the body is open at the rear for facilitating formation of the side guide surfaces, the apparatus further including an insert member for closing the rear of the body and retaining at least one of the actuator means and the catch means within the body, and a clip member for retaining the insert member seated in the body by a pair of interlocking connections with the body. Separation of the insert member from the body requires simultaneous deformation of the clip member at each of the interlocking connections, each interlocking connection being sufficiently flexible so that deflection at only one of the positions does not release the insert member from the body. 
     Preferably the trigger member is rearwardly movable to a stop position wherein the needle projects from about 0.09 inch to about 0.11 inch beyond the trigger surface when the syringe is in the first position for producing shallow penetration by the needle prior to injection of the medicament. The catch means can include a movable ramp member, a forward end of the ramp member being connected at a fixed location on the body, an opposite end of the ramp member engaging a contact surface of the actuator means. The release means can be operative for camming the engagement end of the ramp member out of engagement with the contact surface without disturbing the actuator means in its cocked position until the disengagement from the contact surface is complete. The trigger surface can have an area of about 0.4 square inch, the trigger member activating the release means in response to a force of about 2.0 lbs. from the skin pressure. 
     The receiver means can frictionally limit the forward movement of the syringe by a frictional resistance that is greater than a plunger frictional resistance of the syringe to forward movement of the plunger within the barrel, thus producing a tracked injection by coordinating the forward movements of the plunger and the barrel, a substantial portion of the fluid being deposited along and ahead of the needle during forward movement of the needle into the flesh. For a syringe having a capacity of about 0.5 cc and wherein the frictional resistance is about 0.5 lb., the frictional resistance of the receiver means to the forward movement of the syringe is preferably from about 2 to about 4 lbs. Further, the actuator means can be biased from about 1.5 lbs. to about 4.5 lbs. toward the forward end of the body. Preferably the bias of the actuator means is not more than about 3.0 lbs. for providing a desired level of brain-wave cancellation upon impact of the actuator means against the plunger and for enhancing user comfort. 
     Preferably the injector apparatus includes a safety latch means for preventing operation of the release means except when the syringe is fully seated in the receiver means. The safety latch means can include a movable contact member, means for guiding the contact member between a lock position and an armed position, the contact member being biased toward the lock position, the contact member moving to the armed position in response to seating of the syringe into the receiver means, and means connected to the contact member for preventing movement of the trigger member from the extended position when the contact member is not in the armed position. The contact member can project into the cavity of the guide member in the lock position. 
     In a further aspect of the invention, the actuator means, the catch means, the release means, and the safety latch means are each retained in operative relation to the body by the receiver means being fixedly attached to the body by means of interlocking connection therewith for facilitating assembly of the apparatus and for preventing unauthorized tampering thereof. The connection of the receiver means to the body can be by a pair of finger members of the receiver means outwardly engaging corresponding shoulder surfaces of the body, separation of the finger members from the body requiring simultaneous deformation of both finger members at at least two positions along each of the finger members, the finger members being formed such that localized deflection of the finger members does not bring about release of the receiver means from the body. Thus the present invention provides a low cost, relatively tamper-proof assembly that is disassemblable without damage to its components only when the finger members of the receiver means are each displaced relative to the shoulder surface at at least two independently displaceable locations along each of the finger members. The injector is thus resistant to unauthorized disassembly. Moreover in case of tampering by such unauthorized disassembly, detection of such tampering is facilitated by the claimed configuration wherein proper disassembly may be effected without further damage to components of the injector. 
     The catch means can include a catch member movable between a lock position for preventing forward movement of the actuator means and a release positions, and the release means can be operative for moving the catch member to the release position, whereby the actuator means is not subjected to rearward movement when the release means is being activated. The catch member can further include a first end fixably located relative to the body and a second end movable between a first position preventing the operation of the actuator means and a second position, the catch member in the first position contacts a catch surface of the actuator member. 
     Another aspect of the present invention provides a hypodermic syringe safety injector system including a medical syringe selected from a set of interchangeable syringes, each syringe including a cylindrical barrel having a syringe axis, a lateral projection on the barrel, a hypodermic needle carried by and in fluid connection with one end of the barrel, the needle having a tip extending a fixed distance relative to the lateral projection, a fluid expelling plunger in the barrel and having a portion extending from an opposite end of the barrel; an elongated body for removably holding the syringe, the body having a forward end for the needle and a rearward end for the extending portion of the plunger; a trigger member supported by the body and having a trigger surface projecting forward of the forward end of the body and being adapted for rearward movement from an extended position relative to the body in response to pressure exerted against the trigger surface by the flesh of a patient; receiver means for holding the syringe in axial alignment with the body; stop means for limiting movement of the syringe barrel from a rearward first position to a forward second position relative to the body, the tip of the needle being located rearwardly of the trigger surface in the first position when the trigger member is in the extended position, the needle being projected beyond the trigger surface in the second position for piercing the flesh of a user; means for holding the syringe in lateral alignment with the body during insertion of the syringe into the receiver means, including opposite entry surfaces at a forward extremity of the guide member for laterally centering a contacted portion of the barrel, and rear guide means located rearwardly of the entry surfaces for laterally centering a rear portion of the syringe; actuator means for moving the plunger in a direction toward the forward end of the body; catch means for preventing operation of the actuator means; and release means activated by the trigger member for releasing the catch means, whereby the plunger is projected forwardly within the barrel and the syringe is moved from the first position to the second position in response to movement of the plunger. 
    
    
     DRAWINGS 
     These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description, appended claims, and accompanying drawings where: 
     FIG. 1 is a fragmentary sectional plan view of a safety medicament injector for hypodermic syringes according to the present invention; 
     FIG. 2 is a fragmentary sectional elevational view of the injector of FIG. 1 on line 2--2 of FIG. 1; 
     FIG. 3 is an oblique elevational perspective view of a trigger component of the injector of FIG. 1; 
     FIG. 4 is a fragmentary sectional elevational view as in FIG. 2, showing the injector of FIG. 1 with a conventional hypodermic needle seated therein; 
     FIG. 5 is a fragmentary plan view of the injector of FIG. 1 on line 5--5 of FIG. 4; 
     FIG. 6 is a fragmentary sectional elevational view as in FIG. 4, showing the injector in a partially triggered position; 
     FIG. 7 is a fragmentary sectional elevational view as in FIG. 4 showing the injector at the end of an injection cycle; 
     FIG. 8 is a fragmentary sectional elevational view of the injector of FIG. 2 on line 8--8 of FIG. 2; 
     FIG. 9 is a fragmentary sectional elevational view of the injector of FIG. 2 on line 9--9 of FIG. 2; 
     FIG. 10 is an oblique perspective elevational view of a safety catch component of the injector of FIG. 1 within region 10 of FIG. 1. 
     FIG. 11 is a fragmentary sectional elevational view as in FIG. 2, showing an alternative configuration of the injector of FIG. 1 in an injector system, a syringe of the system being loaded into the injector; 
     FIG. 12 is a fragmentary sectional elevational view of the injector system of FIG. 11 taken on line 12--12 therein; 
     FIG. 13 is a fragmentary sectional elevational as in FIG. 6, showing the system of FIG. 11 in a partially triggered position; 
     FIG. 14 is a fragmentary sectional elevational view of the system of FIG. 11 taken on line 14--14 in FIG. 13; 
     FIG. 15 is a fragmentary sectional elevational view of the system of FIG. 11 taken on line 15--15 in FIG. 13; 
     FIG. 16 is a fragmentary sectional elevational view as in FIG. 14, showing yet another configuration of the system of FIG. 11; and 
     FIG. 17 is an oblique perspective view as in FIG. 3, showing corresponding counterparts of the system of FIG. 11. 
    
    
     DESCRIPTION 
     The present invention is directed to a safety injector for conventional hypodermic syringes. With reference to the drawings, most particularly FIGS. 1-3 and 8-10, an injector 10 includes a body 12 having a base 14 and spaced sides 16. A front cylindrical ring portion 18 of the body 12 slidably receives a cup-shaped trigger member 20, the trigger member 20 having a protruding contact surface 22 and being biased forwardly of the body member 12 by a helical expansion trigger spring 24 that is interposed between the trigger member 20 and a shoulder 26 within the ring portion 18. An opening 28 is formed in the contact surface 22 for permitting a needle 30 of a conventional syringe 32 (shown in FIGS. 4 and 5 and further described below) to protrude the trigger member 20 as further described below. 
     As best shown FIGS. 2 and 3, the trigger member 20 has an elongated release element 34 extending rearwardly therefrom. The release element 34, further described below, is coupled by a boss 35 to the trigger member 20 and guided in rigid relation to the trigger member 20 by a channel 36 that is formed in the base 14 of the body 12. 
     A plunger actuator 38 is slidably guided between the sides 16 and biased forwardly toward the ring portion 18 by a helical expansion plunger spring 40, a rearward end 42 of the plunger spring 40 being located by an insert 44, the insert 44 being supported by a rearward end wall 46 of the body 12. As shown in FIGS. 2 and 8, each side 16 of the body 12 has an inwardly facing shallow longitudinal groove 48 formed therein for retaining in axial alignment the plunger actuator 38, the spring 40, and the insert 44, a forward portion 50 of the spring 40 being guided in axial alignment primarily by a cylindrical boss member 52 of the plunger actuator 38 that extends within the spring 40. An elastic tongue member 54 extends forwardly from the plunger actuator 38 for releasably retaining the actuator 38 in a cocked position shown in FIGS. 1 and 2 by engagement of the tongue member 54 with a pair of latch members 56 that are located on opposite sides of the channel 36. 
     A ramp member 58 is formed in the release element 34 for lifting the tongue member of the actuator 38 out of engagement with the latch members 56 in response to rearward movement of the trigger member 20. 
     Axial movement of the trigger member 20 with respect to the body 12 is limited by a pair of notches 60 that are formed in opposite sides of the release element 34 as shown in FIG. 3, each of the notches 60 being located for contacting opposite ends of a syringe guide block 62 through which the release element 34 passes, the trigger member 20 being movable between an extended position shown in FIGS. 1, 2, and 4 wherein the notches 60 are in contact with a rear surface 64 of the guide block 62, and a retracted position shown in FIG. 7 wherein the notches 60 are in contact with a front surface 65 of the block 62. 
     As shown in FIGS. 4 and 5, the hypodermic syringe 32 includes a cylindrical barrel 66 having a finger flange 68 extending on opposite sides thereof, the needle 30 in fluid communication with the barrel 66, a plunger 70 axially slidable in the barrel 66, the plunger 70 having an external rear end 72 on an extension 74 thereof. The outside of the barrel 66 defines a syringe axis 75. The syringe 32, normally charged with a desired quantity of medicament prior to being loaded into the injector 10, is received with the needle 30 proximate the opening 28 of the trigger member 20, the barrel 66 being locatingly supported by the guide block 62, the guide block 62 being fixedly connected to the body 12 as described below. The sides 16 of the body 12 each have formed therein a recess 76 for receiving the finger flange 64, the recesses 76 defining a limited range of axial movement of the syringe 32 within the guide block 62. As shown in FIG. 9, the guide block 62 forms a longitudinal cavity 78 having an upwardly open slot 80 opposite the base 14 of the body 12, the slot 80 being slightly narrower than the barrel 62 so that the syringe 32 must be snapped into place in the guide block 62. Further, the cavity 78 is formed to have a slight interference fit about the barrel 62 for permitting the axial movement of the syringe 32 only by overcoming a predetermined frictional resistance between the barrel 66 and the guide block 62 as further described below, the cavity 78 defining an injector axis 81 with which the syringe axis 67 is aligned when the barrel 66 is fully seated in the guide block 62. 
     With the syringe 32 in the position shown in FIG. 4, the finger flange 68 is located against a rear surface 82 of each recess 76 and behind a raised detent member 84 that is formed in each side 16 of the body 12 within the respective recesses 76. When the trigger member 20 is pressed against a targeted user&#39;s flesh region 86 as shown in FIG. 6, the trigger member 20 moves axially into the ring portion 18 of the body 12 against the trigger spring 24, the needle 30 slightly protruding the trigger member 20 through the opening 28 thereof for penetrating the flesh region 86. This rearward movement of the trigger member 20 causes the tongue member 54 to be lifted from its engagement with the latch member 56, thereby releasing the plunger actuator 38. Thus released, the plunger actuator 38 is driven forwardly by the plunger spring 40 until it strikes the rear end 72 of the plunger 70. The impact of the actuator 48 against the plunger 70 causes a sudden shock wave to be transmitted into the flesh region 86 by the trigger member 20, momentarily desensitizing the user&#39;s nervous system by brain wave cancellation. The impact also insures that the trigger member 20 becomes fully depressed to the retracted position shown in FIG. 7 and described above. Moreover, the impact acts to dislodge the finger flange 68 from the detent members 84, the detent members absorbing a portion of the impact and amplifying an initial spurt of the fluid medicament for opening a pathway facilitating needle travel and reducing tissue trauma as further described below. 
     The plunger actuator 38, after striking the rear end 72 of the plunger 70, continues toward the ring portion 18, simultaneously moving the plunger 70 forwardly in the barrel 66 and moving the barrel 66, together with the needle 30 and the finger flange 68, forwardly in the guide block until the flange 68 contacts a front surface 83 of the recesses 76 as shown in FIG. 7. This simultaneous movement results from a combination of the frictional resistance of the barrel to axial movement in the guide block 62 being greater than that of the plunger 70 in the barrel 66, and dynamic resistance to the flow of medicament from the needle 30, thereby producing a &#34;tracked injection&#34; whereby at least a substantial portion of the medicament is deposited along and ahead of the advancing needle 30. The tracked injection advantageously causes the elements of the flesh region 86, and especially its delicate blood vessels, to be moved apart ahead of the advancing needle 30, and lubricated by the medicament, thereby reducing tissue damage trauma that would result from cutting by the needle 30. If the plunger 70 is incompletely advanced in the barrel 66 at the conclusion of the forward movement of the barrel 66 as described above, the plunger actuator 38 continues its forward movement against the rear end 72 until such is the case, injecting the remainder of the medicament at the full depth of needle penetration. 
     A feature of the present invention is that the injector 10 can be provided with spacer means 88 for further limiting the travel of the barrel 66 below that which is defined by the cavities 76. The spacer means 88 can include one or more spacer members, designated 88a and 88b in FIGS. 4 and 5. By locating the spacer means 88 in the body 12 between the finger flange 68 and the front surface 83 of the recesses 76, the maximum penetration of the needle 30 into the flesh 86 is reduced from that shown in FIG. 7 by the total thickness of the spacer means 88. 
     Another and important feature of the present invention is that the injector 10 includes a safety catch for preventing premature release of the plunger actuator. As shown in FIGS. 1 and 2, a catch member 90 is interposed between a stop surface 92 of the release element 34 and the guide block 62 as described herein, thereby preventing movement of the trigger member 20 (and the release element 34) whenever the syringe 32 is not fully seated in the cavity 78 of the guide block 62. The catch member 90, shown more clearly in FIG. 10, is a molded plastic part including a relatively rigid, longitudinally oriented upper portion 94, and a pair of downwardly and oppositely extending spring members 96 (designated 96a and 96b) for upwardly biasing the upper portion 94 against a web member 98 of the guide block 62. A pair of upstanding lugs 100 (designated 100a and 100b) of the upper portion 94 retain the catch member 90 against axial movement relative to the guide block 62. The lug 100, together with a forward extension 102 of the upper portion 94, extends between the guide block 62 and the stop surface 92 of the release element 34, thus preventing rearward movement of the trigger member 20. 
     As shown in FIG. 4, when the syringe 32 is seated within the injector 10, the barrel 66 depresses the lugs 100 such that the forward extension 102 of the catch member 90 moves out of alignment with the stop surface 92 of the release element, thereby permitting the rearward movement of the trigger member 20 as shown in FIGS. 6 and 7, the stop surface 92 of the release element 34 passing above the forward extension 102 of the catch member 90. 
     As further shown in FIG. 10, the catch member 90 is formed with stress-relief undercuts 104 (designated 104a and 104b) between the upper portion 94 and the respective spring members 96. Also, the spring member 96a, being directly associated with the forward extension 102, is reinforced by a pin member 106 that is tightly located in the associated undercut of 104a. It has been discovered that the pin member 106 advantageously prevents long-term weakening of the catch member, such as might otherwise be caused by storage of the injector 10 with the syringe 32 received therein. 
     Further according to the present invention, the components of the injector 10 are assembled without conventional fasteners for providing a reliable, inexpensive, tamper resistant product that is adapted for retaining evidence of actual tampering. As best shown in FIGS. 2 and 9, the guide block 62 extends downwardly from its web member 98 on opposite sides of the release element 34 (into the notches 60) and through an opening 108 in the base 14 of the body 12. A lower portion of the opening 108 is enlarged toward opposite sides of the body 12, forming a pair of shoulders 110, the downward extension of the guide block 62 forming a pair of hooked fingers 112 that engage the shoulders 110, thereby securing the guide block 62 in fixed relation to the body 12. A pair of upwardly inclined chamfers 114 are formed at opposite sides of the opening 108 for facilitating insertion of the guide block 62 into the body 12, the fingers 112 snapping into engagement with the shoulders 110 when the guide block 62 is fully seated therein. The fingers 112 are formed with a lower contour that is approximately flush with the bottom of the base 14 for preventing unauthorized disassembly of the guide block 62 from the body 12. The installation of the guide block 62 is the last step in assembly of the injector 10, the other parts, particularly the trigger member 20, the trigger spring 24, the release element 34, the plunger actuator 38, the plunger spring 40, the catch member, and the pin member 106, are securely locked in assembled relation to the body 12 with the guide block 62 in place. 
     A preferred order of assembly is to first slide the insert 44, the plunger spring 40, and the actuator 38 rearwardly from the proximate recesses 76 into engagement with the grooves 48 of the body, then slide the trigger spring 24, the release element 34 and the trigger member 20 (with the boss 35 of element 34 engaging the trigger member 20) rearwardly into the ring portion 18 of the body 12, the element 34 extending into the channel 36. The catch member 90 is separately located between the fingers 112 of the guide block 62 with the pin member 106 in place, the pin member 106 having a free length slightly greater than a spacing between the fingers 112 for temporarily holding the catch member 90 therebetween. Finally, with the plunger actuator 38 and the trigger member 20 held rearwardly against the biasing by the respective springs 40 and 24, the guide block 62 (with the catch member 90 and the pin member 106 in place) is lowered into the body 12 and snapped into the opening 108. 
     Disassembly is possible only by bending the fingers 112 inwardly from engagement with the shoulders 110 while upwardly urging the guide block 62 from the opening 108. Such disassembly is discouraged in that simultaneous inward movement of both fingers 112 is required, substantially along a full axial length thereof because the fingers are formed with sufficient longitudinal flexibility that full inward movement at only one location does not release the finger 112 from the entire length of the associated shoulder surface 110. Also, the inward deflection of the fingers 112 is limited by the release element 34 being located between the fingers 112. Attempts to accomplish this disassembly with ordinary tools such as a screwdriver or conventional pliers is expected to result in defacement of the body 12 and/or the fingers 112 by surface damage resulting from the tools digging into the respective parts of the injector 10. For factory disassembly, a special tool such as pliers having thin jaws that extend between the body 12 and the fingers 112 along the full length of the fingers 112 can be fabricated, such pliers not being commonly available. 
     The tracked injection feature of the present invention is obtained by close control of the interference fit between the cavity 78 and the barrel 66 of the syringe 32, in combination with a desired force profile of the plunger spring 40. For this purpose, the walls 16 advantageously reinforce the guide block 62 by contacting a pair of protrusions 116 that are formed on opposite sides of the guide block 62 at the tops of the respective walls 16. The reinforcement by the walls 16 can be controlled by the relatively inexpensive expedient of varying a thickness T of each protrusion 116. 
     In a preferred exemplary embodiment of the present invention for use with a standard 1/2 cc syringe, the trigger member is about 0.8 inch in diameter, having a travel of about 0.13 inch against a bias of about 0.5 lb. from the trigger spring 24, a maximum trigger force of about 2.5 lbs. being required. The plunger spring 40 provides a bias of approximately 3.25 lbs. against the plunger actuator 38 thereon, the bias decreasing to approximately 1.5 lbs. at the position shown in FIG. 7, the actuator 38 traveling approximately 2.3 inches between the positions shown in FIGS. 4 and 7. The force required to move the plunger 70 forwardly in the barrel 66 for expelling fluid is about 0.5 lbs., and the frictional force required for moving the barrel 66 forwardly in the cavity 78 is about 2.75 lbs. The force required to depress the catch member 90 during insertion of the syringe barrel 66 into the cavity 78 is approximately 1 lb. The resistance of the guide block 62 to upward movement of the barrel 66 from the cavity is about 3.5 lbs., about 2.5 lbs. being required for removal as assisted by the approximate 1 lbs. force from the catch member 90. The maximum bias provided by the plunger spring 40 for producing the tracked injection can be from about 2.5 lbs. to about 4.5 lbs. However, it is preferred to limit the bias to not more than about 3.5 lbs. for effective brain-wave cancellation upon impact of the actuator 38 with the plunger 70. 
     The present invention provides a safe and convenient solution to the problem of administering injections by those not having specialized medical training. The injector 10 can easily be operated by the person receiving the injection, using only one hand, and the targeted flesh region 86 does not need to be in view. Moreover, the injection is quick and painless, and conventional aspiration of the syringe 32 is not needed. 
     For conventional syringes in other sizes, the present invention provides that separate embodiments of the injector 10 be made for each standard size of the syringe 32. Thus the reliability of the injector 10 is not compromised by adjustments that would otherwise be needed in adapting to different sizes of the syringe 32. The separate embodiments can be color coded for ease of identification. 
     The springs 24 and 40 are fabricated from a suitable spring-tempered material such as corrosion-resistant steel. The other parts of the injector 10 are preferably molded from a suitable plastic material for light weight and ease of fabrication. Suitable plastic materials for the injector 10 include ABS, polycarbonate, and acetyl. A particularly advantageous material for the pin member 106 is nylon which is commonly available for use as fishing line, approximately 0.022 inch in diameter. 
     In the exemplary preferred embodiment of the injector 10, the catch member 90 has a width W of 0.1 inch, the fingers 112 are spaced apart by a distance S of 0.125 inch, and the pin member 106 has a length L of 0.130 inch. Thus the catch member 90 is free to move vertically between the fingers 112, yet the member 90 is retained in place during assembly by a slight interference fit between the ends of the pin member 106 and the fingers 112. A quick and effective method for fabricating the pin member 106 without expensive tooling and set-up expense includes the steps of axially inserting a length of the 0.022 diameter material into the undercut 104a with one end of the material flush with a side of the catch member 90, then shearing the material using a pair of scissors 118, one blade of which is located against the opposite side of the catch member 90, the blade having a thickness of 0.030, the excess of the length L over the width W. 
     With reference to FIGS. 11-17, in a further embodiment of the injector 10 the body 12 is reconfigured for improved dimensional stability of the spacing between the sides 16, so that the body can be injection molded to include the grooves 48, for example, without either a compound mold mechanism or requiring that the sides 16 be sprung apart during removal from the mold. Accordingly, the body 12 is open at the rear, being formed without the end wall 46. Instead, a counterpart of the insert 44, designated 44&#39; in FIGS. 11-16, forms a rear end portion of the injector 10. The insert 44&#39; is formed to include an opposing pair of vertically oriented, outwardly extending insert dovetails 120 that slidably engage corresponding grooves of the body 12. The insert 44&#39; is secured in a downwardly seated position within the body 12 by means of a generally U-shaped spring clip member 122 that partially encloses a boss member 124 of the insert 44&#39;, the boss member 124 also serving to locate a rear extremity of the plunger spring 40. Opposite leg extremities 126 of the clip member 122 are each formed to include a catch member 128, the catch member 128 snapping into engagement with corresponding catch surfaces 130 of the body 12 when the insert 44&#39;, together with the clip member 122, is fully seated in the body 12. As best shown in FIGS. 13-15, an exemplary configuration of the clip member 122 has the leg extremities 126 sloping forwardly and downwardly away from the insert 44&#39; , the catch surfaces 130 of the body 12 being positioned rearwardly of the leg extremities 126. As the insert 44&#39; is lowered into is seated position, the leg extremities 126 of the clip member 122 are deflected forwardly until the catch members 128 snap rearwardly into engagement with the catch surfaces 130. The forward deflection of the extremities 126 can be accomplished by elastic deformation of the clip member 122, with or without an accompanying deflection of the spring 40. 
     In order to effect disassembly of the insert 44&#39; from the body 12, it is required according to the present invention that the catch members 128, which are formed flush with the body 12, be simultaneously moved forwardly while overcoming spring resistance of the clip member 122. The injector 10 is thus secured against unauthorized tampering in that the simultaneous displacement of the leg extremities as required for disengaging the catch members is very difficult, even using suitable instruments such as jeweler&#39;s screwdrivers; moreover, the use of such instruments would almost certainly cause noticeable marring of the clip member 122 and/or the body 12. Authorized disassembly can be effected by use of a forked blade member 132 that is specially configured for simultaneously camming the catch members 128 away from the catch surfaces 130. Preferably, and as further shown in FIG. 14, an anchor connection 134 between the clip member 122 limits or prevents &#34;crosstalk&#34; between the leg extremities (disengagement of one catch member tending to cause disengagement of the other). Further, the clip member 122 can be formed integrally with the insert 44&#39; for reducing the parts count and facilitating assembly of the injector 10. 
     As shown in FIG. 16, a preferred alternative configuration of the clip member 122 has the catch members 128 facing outwardly, the catch members 128 being deflected towards each other during assembly and snapping outwardly as the insert 44&#39; is fully seated. As shown in FIG. 16, the catch surfaces 130 of the body 12 are preferably oriented with a slight lateral inclination for avoiding any tendency of the leg extremities 126 to move together in response to a force upwardly applied to the insert 44&#39;. 
     In further accordance with the present invention, the plunger actuator, designated 38&#39; in FIGS. 11 and 13, is formed without the tongue member 54, the actuator 38&#39; being retained in its rearward, cocked position by a flexible, cantilevered incline member 136. A forward end portion of the incline member 136 is fixably located within the body 12 by a base insert 138, the insert 138 forming a longitudinal dovetail connection with the body 12, being retained axially therein by the insert 44&#39;. 
     A counterpart of the release element 34, designated 34&#39; in FIGS. 11-13 and 17, forms a downwardly facing release surface 140 that drives the incline member downwardly out of engagement with the plunger actuator 38&#39; as the trigger member 20 is moved rearwardly, thereby triggering the injector 10 as further described above. When the actuator 10 is cocked, prior to triggering, the incline member preferably slopes at an angle A of approximately 10 degrees from the injector axis 81. Further, the actuator 38 is formed with a contact surface 142 that is engaged by the incline member 136 in the cocked condition, the contact surface 142 being similarly inclined by approximately 10 degrees from being normal to the injector axis 81, for permitting movement of the incline member 136 from the cocked to the triggered position without producing axial movement of the actuator 38&#39; during such movement. The rear extremity of the incline member is also formed square with the sides thereof, for full engagement with the contact surface 142. In an experimental prototype of the injector incorporating the release element 34&#39; having the release surface 140, the plunger actuator 38&#39; having the contact surface 142, and the incline member 136, the trigger force was advantageously reduced from 2.5 pounds to approximately 2.0 pounds. Further, it is believed that the combination of the incline member 136, the release surface 140 and the contact surface 142 as described herein is operative at significantly reduced variation of the trigger force, in multiple uses of the injector 10, as well as from unit to unit. Moreover, in combination with the trigger force operation at approximately 2.0 lbs., it is preferred that the maximum bias provided by the plunger spring 40 be reduced to not more than approximatedly 3.0 lbs. for greater user comfort. 
     In the configuration of FIGS. 11-17, insertion of the syringe 32 into the injector 10 is facilitated in several ways according to the present invention. As shown in FIGS. 11-13, the syringe 32 may be brought into engagement with the injector 10 by first resting the syringe 32 with the finger flange 68 contacting upper guide surfaces 144 of the sides 16, the barrel 66 resting against forward extremities of a pair of entry surfaces 146 at an intersection of the slot 80 with the top of the guide block 62. Further, the finger flange 68 is formed with a projection 148 that extends downwardly between the sides 16 of the body 12, opposite ends of the projection 148 being laterally guided between inside surfaces 150 of the sides 16 for maintaining the syringe 32 laterally aligned with the injector 10 as the syringe is moved forwardly, the barrel 66 sliding along the entry surfaces 146 as the finger flange 68 is being guided by the upper guide surfaces 144 and the inside surfaces 150 of the body 12. The widely spaced contacts between the syringe 32 and the injector 10 advantageously impart stability to the operation of bringing the parts into engagement, and the further operation of moving the syringe 32 forwardly to its seated position. More particularly, the initial engagement of the syringe 32 with the injector 10 is depicted by the dashed lines 32a in the drawings. Forward movement of the syringe 32 to just prior to entry of the finger flange 68 into the recesses 76 is depicted by the dashed lines 32b. Further movement of the syringe 32 such that the finger flange 68 just enters the recesses 76 is depicted by the dashed lines 32c. In this position, the syringe axis 75 is parallel to the injector axis 81, the barrel 66 extending partially into a clearance notch 152 that is formed in the trigger member 20, the needle 30 also protruding an enlarged counterpart of the opening 28, designated 28&#39; in FIG. 11. 
     With the syringe 32 in the position 32c, the final positioning thereof with the barrel 66 seated in the cavity 78 of the guide block 62 (as indicated by the dashed lines 32d) is completed by first pressing the barrel 66 downwardly, preferably at a point proximate the forward extremity of the guide block 62 for easily lowering a forward portion of the barrel 66 into the block 62. As the barrel 66 enters the slot 80, the downward pressure is applied increasingly rearwardly along the barrel 66 for lowering the barrel 66 into the block 66 along the full length of the slot 80, the finger flange 68 also being lowered into the cavities 76 at the rearward extremity thereof. As the barrel 66 enters the cavity 78, the syringe 32 snaps into its fully seated position as further described above. Moreover, the cavities 76 are advantageously located at a height for supporting the finger flange 68 proximately aligned with the syringe axis 81, whereby excess downward pressure thereon (which might be inadvertently applied) does not result in upward movement of the forward portion of the barrel 66 that might otherwise be caused by pivoting of the barrel 66 about the rearmost extremity of the cavity 78. Accordingly, the finger flange 68 is formed with a depth d on opposite sides of the syringe axis 75, the depth d defining the height of the syringe axis above the upper guide surfaces 144 at the finger flange 68 between the positions 32a and 32b, and the cavities 76 are formed with a depth d&#39; below the injector axis 81, the depth d&#39; being the same as or very slightly greater than the depth d. Preferably the parts are formed such that the maximum difference between d&#39; and d is not greater than the elastic deformation between the barrel 66 and the body 12 at the cavities 76 behind the guide block 62 resulting from a downward force applied to the finger flange 68, the downward force being just insufficient to raise the forward portion of the barrel 66 from its seated position. In practice, is has been found that such maximum difference is approximately 0.005 inch using the syringe 32 having a capacity of 0.5 cc, as otherwise described above. Also, the syringe 32 is formed with the finger flange having the same depth d opposite (above) the syringe axis 75 for allowing the syringe 32 to be properly seated without regard to whether it is inverted. 
     Although the present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions are possible. Therefore, the spirit and scope of the appended claims should not necessarily be limited to the description of the preferred versions contained herein.